The present invention relates to a process for manufacturing a decorative mainly isometric thermosetting laminate, a decorative thermosetting laminate obtained by the process, and use thereof.
Products clad with thermosetting laminates are quite common nowadays. They are most often used where the demand for abrasion resistance is great but also where resistance towards different chemical substances and moisture is required. Floors, floor skirtings, work tops, table tops, doors and wall panels can serve as an examples of such products. The thermosetting laminate is most often made from a number of base sheets and a decorative sheet placed closest to the surface. The decorative sheet may be provided with the desired decor or pattern. Thicker laminates are often provided with a core of particle board or fibre board where both sides are covered with sheets of thermosetting laminate. The outermost sheet is, on at least one side, most often a decorative sheet.
One problem with such thicker laminates is that the core is much softer than the surface layer which is made from paper impregnated with thermosetting resin. This will cause a considerably reduced resistance towards thrusts and blows compared to a laminate with a corresponding thickness made of paper impregnated with thermosetting resin only.
Another problem with thicker laminates with a core of particle board or fibre board is that these normally will absorb a large amount of moisture, which will cause them to expand and soften whereby the laminate will warp. The surface layer might even, partly or completely come off in extreme cases since the core will expand more than the surface layer. This type of laminate can therefore not be used in damp areas, such as wet rooms, without problem.
The problems can be partly solved by making the core of paper impregnated with thermosetting resin as well. Such a laminate is most often called compact laminate. These compact laminates are, however, very expensive and laborious to obtain as several tens of layers of paper have to be impregnated, dried and put in layers. The direction of the fibre in the paper does furthermore cause a moisture and temperature difference relating expansion. This expansion is two to three times as high in the direction crossing the fibre than along the fibre. The longitudinal direction of the fibre is coinciding with the longitudinal direction of the paper. One will furthermore be restricted to use cellulose as a base in the manufacturing though other materials could prove suitable.
The above problems have through the present invention been solved whereby a flexible process for the manufacturing of a mainly isometric thermosetting laminate has been achieved where the process easily can be adapted regarding cost efficiency, impact resistance, rigidity, density, moisture absorption, expansion, mould resistance and fire resistance. The invention relates to a process for the manufacturing of a decorative mainly isometric thermosetting laminate comprising an isometric core, a primary surface layer and optionally a secondary surface layer. The invention is characterised in that 85 parts by weight of preferably organic particles, which particles have an average particle size in the range of 5-3000 xcexcm, preferably 5-2000 xcexcm, are mixed with 15-85 parts by weight, preferably 22-37 parts by weight, of a thermosetting resin in the form of a powder which resin is selected from the group of phenol-formaldehyde resins, melamine-formaldehyde resins, urea-formaldehyde resins or mixtures thereof. The mixing takes place in for example an extruder where the mixture is kneaded powerfully so that friction heat is formed. It is also possible to use a calendar mill for the same purpose. The friction heat is not allowed to exceed 150xc2x0 C., preferably below 110xc2x0 C., most preferably below 90xc2x0 C. The thermosetting resin is thereby bonding to or impregnating the particles by becoming soft. The particles that possibly are joined by the thermosetting resin are divided and an agglomerate of thermoplastic resin and particles is formed. The agglomerate has an average particle size of 200-3000 xcexcm and a resin content of 10-50% by weight, preferably 20-30% by weight.
The particle/resin mixture is thereafter dried to a water content below 10% by weight, preferably below 5% by weight.
The dried particle/resin mixture is thereafter evenly distributed on a carrier, a pressing belt of a continuous laminate press or on a press plate of a discontinuous laminate press. The dried particle/resin mixture is thereafter continuously or discontinuously compressed at a temperature of 60-120xc2x0 C., preferably 80-100xc2x0 C. and a pressure of 15-400 bar, preferably 30-120 bar so that the particle/resin agglomerate flow out without completely curing the resin. A pre-fabricate to an isometric core is hereby obtained. The core pre-fabricate is then fed between the press belts of a continuous laminate press, or is placed on a press plate of a discontinuous laminate press, together with a primary surface layer which is provided with a decorative layer, and optionally a secondary layer and is thereafter continuously or discontinuously compressed at a temperature of 120-200xc2x0 C., preferably 140-180xc2x0 C. and a pressure of 15-300 bar, preferably 30-150 bar so that the resin cures, whereby a decorative thermosetting laminate provided with an isometric core is obtained.
According to another alternative the above achieved dried particle resin/mixture is evenly distributed on a carrier, a press belt of a continuous laminate press or on a discontinuously compressed at a temperature of 120-200xc2x0 C., preferably 140-180xc2x0 C. and a pressure of 15-300 bar, preferably 30-150 bar so that the resin cures, whereby an isometric core is formed. The core is provided with a primary surface layer and optionally a secondary surface layer in connection to or after the pressing.
A pressure in the range 15-70 bar is usually used in a continuous pressing process while a pressure in the range of 50-400 bar is used in discontinuous pressing.
The particles are suitably completely or partly constituting of wood parts or fruit parts from plants, whereby the wood parts for example include saw dust, wood powder or finely chopped straw while the fruit parts suitably consists of some kind of cereal in the form of flour, for example corn wheat or rice flour. The particles may also completely or partly consist of recycled material such as waste paper, cardboard or rejects from thermosetting laminate manufacturing. The particles may furthermore be completely or partly made of lime. The particles are thereby selected by the characteristics they will give the finished laminate. Mixtures of different particles will also give favourable characteristics. The particles are suitably dried to a water content of below 10% by weight, preferably below 6% by weight, before the mixing.
The dried particle/resin mixture is preferably distributed so that the difference in particle weight per area unit of the surface of the intended core doesn""t exceed 10%, preferably below 3%. The particle/resin mixture is for example distributed on a press plate to a discontinuous multiple opening press. The press plate can be provided with a detachable frame which surrounds the prospective core. The frame might alternatively be attached to the press plate whereby the frame and the plate forms a tray. A second press plate with dimensions smaller than the inner dimensions of the frame is placed on top of the distributed particle/resin mixture in the alternatives where a frame is used. A number of press plates provided with frames and containing particle/resin mixture with a second press plate on top are placed on top of each other and are moved to the laminate press. The second press plate is cancelled in cases where a press plate without frame is used. The procedure otherwise corresponds to the above described procedure with a frame.
The dried particle/resin mixture can also be pressed in a continuous laminating procedure. The particle/resin mixture is then distributed on, for example, a carrier in the form of a web which is continuously feed between two steel belts in a continuous laminate press. The carrier is removed after the passage through the laminate press. The carrier may also be constituted by the primary or the secondary layer whereby the carrier not is separated from the laminate since it forms a part thereof.
The pressing process is suitably initiated with a low initial pressure, preferably 10-50% of the final pressure during which initial pressure the particle/resin mixture is allowed to flow as the resin softens due to the temperature. The pressure is gradually increased before curing starts, which depending on setting agent composition, pressure and temperature takes around 5-120 seconds. The temperature is suitably 100-200xc2x0 C., preferably 140-170xc2x0 C. while the pressure is 10-500 bar, preferably 10-300 bar with a final pressure of 100-300 bar during a discontinuous pressing procedure. The temperature is suitably 120-200xc2x0 C., preferably 140-180xc2x0 while the pressure 10-300 bar, preferably 10-150 bar with a final pressure of 50-150 bar during a continuous pressing procedure. The initial pressure, the final pressure and the temperatures are in both cases depending on particle size, particle composition and resin composition.
The primary surface layer is preferably made from at least one or more decorative papers, for example xcex1-celluloce impregnated with thermosetting resin, preferably melamine-formaldehyde resin and/or urea-formaldehyde resin. One or more so-called overlay paper sheets, impregnated with melamine-formaldehyde resin or urea-formaldehyde resin are optionally placed on top of the decorative paper. One base paper, impregnated with thermosetting resin preferably melamine-formaldehyde resin, urea-formaldehyde resin, phenol-formaldehyde resin or mixtures thereof is optionally placed under the decorative paper. A diffusion preventing foil is optionally placed under the decorative paper, closest to the core.
It is in certain cases desirable to place a secondary surface layer on the opposite side of the core. The secondary surface layer then suitably consists one or more conventional so-called base papers impregnated with thermosetting resin, preferably phenol-formaldehyde resin or urea-formaldehyde resin. The base paper is intended to counteract warping of the laminate which otherwise could be caused by differences in moisture and temperature related expansion between the core and the surface layer. The secondary surface layer can alternatively consist one or more decorative papers, for example of xcex1-cellulose, impregnated with thermosetting resin, preferably melamine-formaldehyde resin or urea-formaldehyde resin. According to yet another embodiment the secondary surface layer consist of a diffusion preventing foil placed closest to the core.
The diffusion preventing foil is preferably made of a metal such as aluminium, steel, copper, zinc or of a plastic material such as polyethylene, polypropylene polyalkylene-terephthalate, acrylic polymers, polyvinyl chloride, fluorinated thermoplastic materials or the like. The surfaces of the diffusion preventing foil are suitably treated by being coated with a primer, micro-etched, blasted, corona treated, spark milled, brush-plated, electro-plated or the like so that the adhesion to the impregnated papers and carrier layer respectively is increased by surface enlargement or surface activation. The foil suitably have a thickness of 5-2000 xcexcm, preferably 10-1000 xcexcm. Foils of metal suitably have a thickness of 5-200 xcexcm, preferably 10-100 xcexcm while foils of thermoplastic material have a thickness of 0.2-2mm, preferably 0.3-1 mm. The thermal coefficient of expansion of the foil is suitably in the range 15xc3x9710xe2x88x926/xc2x0 K and 100xc3x9710xe2x88x926/xc2x0 K, preferably between 15xc3x9710xe2x88x926/xc2x0 K and 50xc3x9710xe2x88x926/xc2x0 K. It is desirable to use a foil with a thermal coefficient of expansion as close as possible to the thermal coefficient of expansion of the thermosetting resin impregnated paper since large differences will cause inner tensions on temperature changes, which might cause de-lamination between the foil or the foils and the other layers. These inconveniences are especially notable at lamination and when cooling the laminate after lamination. It might, however, be desirable in certain applications to select a foil with a temperature depending expansion deviating substantially from the other materials of the laminate. One such application might for example be a non-symmetric laminate where the foil would counteract the temperature depending warping which otherwise would occur in the non-symmetrical laminate. The thermal coefficient of expansion for the usual types of phenol-formaldehyde based laminates lies in the range 15xc3x9710xe2x88x926/xc2x0 K-40xc3x9710xe2x88x926/xc2x0 K. This value can be effected by, among other, changes in resin content, paper quality and fibre direction but also time, pressure and temperature during pressing. By selecting foils with a suitable thickness and thermal coefficient of expansion, the differences in expansion between the various materials included in the laminate can be adapted whereby the temperature-depending warping can be completely avoided, even in non-symmetrical laminates.
The thermosetting laminate may suitably, at discontinuous pressing, be provided with three-dimensional structures such as, for example, groove, tenon and/or lath-work. It becomes possible to partly, or completely, avoid subsequent treatment by providing the laminate with functional parts during the pressing. The laminate may also be provided with a reinforcing lath-work on the rear side. It has until now not been possible to achieve such functional parts using conventional processes. A foil must be of a limb and ductile kind if a diffusion preventing foil is to be applied to such a rear side. As examples of such foils can be mentioned ductile aluminium foil, annealed copper foil or a thermoplastic foil.
The invention also relates to a thermosetting laminate obtained by the process. The thermosetting laminate is mainly isometric with a difference in coefficient of expansion, between the length and cross direction of the laminate, of below 10%. The thermosetting laminate has suitably an ability to absorb water which is lower than 10% by weight, preferably lower than 6% by weight, after 100 h in water at 23xc2x0 C.
The thermosetting laminate has furthermore an impact resistance greater of than 2 kJ/m2, preferably greater than 3 kJ/m2. At least one thermosetting resin impregnated paper, preferably the uppermost, is coated with hard particles of, for example, silicon oxide, aluminium oxide and/or silicon carbide with an average size of 1-100 xcexcm, preferably 5-60 xcexcm in cases where a thermosetting laminate with a high abrasion resistance is desired.
The invention also relates to the use of a thermosetting laminate obtained by the process. The thermosetting laminate may hereby be used as a lining on floors, inner walls, ceilings, and doors in dry as well as wet rooms. The thermosetting laminate may also be used as table tops, work tops, facade boarding and roofs.